1. Field of the Invention
The present invention relates to an illumination structure for a pushbutton.
2. Description of the Related Art
Many devices including electronic devices which are required to be electrically operated have pushbuttons as function keys. Depending on environments and conditions in which to use pushbuttons, there are employed illuminated pushbutton switches with a lamp disposed in the switch. For example, illumination structures for pushbuttons are disclosed in Japanese laid-open utility model publications Nos. 4-8223, 6-33335, 6-68257, and Japanese laid-open patent publication 2002-8478. The illumination structure disclosed in Japanese laid-open utility model publication No. 4-8223 has a button and a protrusion on a lower side thereof which are integrally formed with a sheet. The protrusion on the lower side of the button directly presses a membrane switch or an electrically conductive contact. Light that is emitted from a light-emitting body disposed laterally of the protrusion passes through a diffusion plate and illuminates a lower slanted surface of the button. According to the illumination structure disclosed in Japanese laid-open utility model publication No. 6-33335, a presser disposed on a lower side of a lever-shaped button directly presses a click spring into contact with a contact. An LED is disposed closely to a hinged portion of the lever, and emits light that is applied through a curved surface of the lever below the hinged portion into the lever. According to the illumination structure disclosed in Japanese laid-open utility model publication No. 6-68257, a boss is mounted on a reverse surface of a button and constricted downwardly. The tip end of the boss presses a plunger of an illumination switch with an LED device housed therein, into contact with a contact. The illumination structure disclosed in Japanese laid-open patent publication No. 2002-8478, a key top has a lower flat surface for directly pressing a diaphragm contact. Light emitted from LEDs which are disposed around the key top enters the key top from a flat surface formed on the side of a key flange.
The above illumination structures, which are arranged such that the pushbutton directly presses the switch, are disadvantageous in that they are structurally complex and their components are of complicated shape.
To solve the above problems, there has been employed a simple illumination structure in which a light-transmissive soft rubber sheet having a presser for pressing a metal sheet contact is disposed over the entire surface of the button, and a key top molded of a transparent resin disposed in an opening of a front case is bonded to the rubber sheet. The key top can press the presser, and a side of the presser receives light emitted from light-emitting element disposed around the presser to illuminate the key top through the presser.
FIG. 1 of the accompanying drawings is a fragmentary cross-sectional view of a first conventional illumination structure for a pushbutton, which comprises a combination of a rubber sheet and a key top in an electronic device. A pushbutton switch mechanism of the electronic device has key top 72 molded of a transparent resin, light-transmissive soft rubber sheet 74 covering the pushbutton switch in its entirety, metal sheet contact 76, and light-emitting elements 77. Key top 72 has a flange engageable with an edge of an opening in a front case 71 of the electronic device for sliding movement only into the pushbutton switch. Rubber sheet 74 is secured to front case 71 and has presser 75 formed on its surface remote from key top 72 in positional alignment with key top 72. Key top 72 has a lower surface bonded to the upper surface of rubber sheet 74. Metal sheet contact 76 is disposed on board 78 at a position aligned with presser 75. Light-emitting elements 77 are disposed on board 78 in positions around presser 75.
With the above conventional illumination structure, as shown in FIG. 1, presser 75 formed on rubber sheet 74 for pressing metal sheet contact 76 is of a conical shape whose side surface has a large angle with respect to its bottom surface and hence has a small area. Therefore, light emitted from light-emitting elements 77 is applied laterally to the side surface of presser 75 of rubber sheet 74, so that only the side surface of the presser, indicated by the reference character D in FIG. 1, to which light is applied becomes highly illuminated. FIG. 2 of the accompanying drawings is a schematic view of conventional pushbutton 12 shown in FIG. 1, as seen from above. Since the area of the side surface of the conventional presser as seen from the above is small, when the illumination structure is viewed from outside thereof, as shown in FIG. 2, only the region corresponding to the side surface of the presser, which is shown hatched, provides a highly bright area E.
Other than the above structure in which the soft rubber sheet is bonded to the key top of a transparent resin, there is also employed a pushbutton illumination structure which uses a key sheet of the film type that comprises a thin film filled with a resin, rather than individual key tops.
FIG. 3 of the accompanying drawings is a fragmentary cross-sectional view of a second conventional illumination structure for a pushbutton, which comprises a combination of a rubber sheet and a key sheet in an electronic device. A pushbutton switch mechanism of the electronic device has a key sheet comprising transparent thin film 82 and light-transmissive filler resin 83 and covering the pushbutton in its entirety beneath front case 81, light-transmissive soft rubber sheet 84 disposed below the key sheet in covering relation to the overall key sheet, metal sheet contact 86 disposed on board 88, and light-emitting elements 87 disposed on board 88. Filler resin 83 of the key sheet is filled in a cylindrical shape in film 82 so as to have an upper surface projecting into film 82 to push film 82 upwardly within an opening in front case 81, thus providing a key surface, and a lower surface projecting as presser 85 from the film surface. Metal sheet contact 86 is disposed in a position aligned with presser 85, and light-emitting elements 87 are disposed in positions around presser 85.
With the above conventional illumination structure, too, as shown in FIG. 3, presser 85 of filler resin 83 for pressing metal sheet contact 86 is of a conical shape whose side surface has a large angle with respect to its bottom surface and hence has a small area. Therefore, light emitted from light-emitting elements 87 is applied laterally to rubber sheet 84 on the side surface of presser 85 of filler resin 83, so that only rubber sheet 85 on the side surface of the presser, indicated by the reference character F in FIG. 3, to which light is applied becomes highly illuminated. Consequently, when the illumination structure is viewed from outside thereof, as shown in FIG. 2, only the region corresponding to the side surface of the presser, which is shown hatched, provides a highly bright area E in a partial round pattern.